Semiconductor structure and fabricating method thereof

ABSTRACT

A semiconductor structure and a method of fabricating the semiconductor structure are provided. The semiconductor structure includes a substrate; a metal gate structure on the substrate; and a spacer next to the metal gate structure having a skirting part extending into the metal gate structure and contacting the substrate. The metal gate structure includes a high-k dielectric layer and a metal gate electrode on the high-k dielectric layer.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a continuation of the application Ser. No.14/478,915, filed on Sep. 5, 2014, which is incorporated herein byreference in its entirety.

BACKGROUND

Manufacturing of an integrated circuit (IC) has been largely driven bythe need to increase the density of the integrated circuit formed in asemiconductor device. This is typically accomplished by implementingmore aggressive design rules to allow larger density of IC device to beformed. Nonetheless, the increased density of the IC devices, such astransistors, has also increased the complexity of processingsemiconductor devices with the decreased feature sizes.

Transistors in the integrated circuit have typically been formed with asilicon gate oxide and polysilicon gate electrode. There has been adesire to replace the silicon gate oxide and polysilicon gate electrodewith a high-k gate dielectric and metal gate electrode to improve deviceperformance as feature sizes continue to decrease. Transistor havingmetal gate electrode, especially in conjunction with high dielectricconstant (high-k) dielectric, may address issues such as polysilicondepletion and gate leakage associated with silicon gate oxide. Inaddition, metal gate transistors exhibit a lower resistivity than dopedpolysilicon. In the manufacturing process of the metal gate transistors,further improvements are constantly necessary to satisfy the performancerequirement in the scaling down process.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of a semiconductor structure, inaccordance with some embodiments.

FIGS. 2A-2I are various cross-sectional views of a method of fabricatinga semiconductor structure, in accordance with some embodiments.

FIG. 3 is a flow chart of the method of fabricating a semiconductorstructure, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In some embodiments, a gate structure includes a gate oxide layer over asubstrate, and a gate electrode and two spacers adjacent to the gateelectrode formed over the gate oxide layer. In a metal gate transistorfabricating process, a “gate last” or a “replacement gate” methodologyis used. In such a process, a dummy (e.g., sacrificial) gate electrode,which may include polysilicon, is initially formed, various processesassociated with the semiconductor device are performed, and the dummygate electrode is subsequently removed and replaced with a metal gateelectrode. When removing the dummy gate electrode, the gate oxide layerunder the dummy gate electrode is also removed and replaced with ahigh-k dielectric layer, but the gate oxide layer under the spacers mayalso be removed, and a tunnel under the spacers may be formed. A metalleakage issue is therefore formed when forming the metal gate electrode.The metal deposited between the spacers leak to a source/drain region,which may include an epitaxy, through the tunnel under the spacer. Andthe formed metal gate electrode may have voids in the metal gateelectrode, thus affects the transistor performance.

Referring to FIG. 1, FIG. 1 is a cross-sectional view of a semiconductorstructure, in accordance with some embodiments. A semiconductorstructure 100 includes a substrate 110. A metal gate structure 120 onthe substrate 110. A spacer 130 next to the metal gate structure 120having a skirting part 132 extending into the metal gate structure 120.An epitaxy 140 next to the spacer 130. The semiconductor structure 100may be intermediate structures fabricated during processing of anintegrated circuit, or portion thereof, that may include static randomaccess memory (SRAM) and/or other logic circuits, passive componentssuch as resistors, capacitors, and inductors, and active components suchas P-channel field effect transistors (PFET), N-channel FET (NFET),metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolartransistors, high voltage transistors, high frequency transistors, othermemory cells, and combinations thereof. In some embodiments, thesubstrate 110 may be a silicon substrate. The substrate 110 may includevarious doping configurations depending on design requirements as isknown in the art (e.g., p-type substrate or n-type substrate). Thesubstrate 110 may include various doped regions, such as source/drainregions, n-well, p-well, and may include shallow trench isolation (STI)regions. The substrate 110 may include a compound semiconductor such as,silicon carbide, gallium arsenide, indium arsenide, or indium phosphide.The metal gate structure 120 includes a high-k dielectric layer 122 onthe substrate 110, and a metal gate electrode 124 on the high-kdielectric layer 122. The metal gate electrode 124 may include, tungsten(W), aluminum (Al), titanium (Ti), titanium nitride (TiN), tantalum(Ta), tantalum nitride (TaN), cobalt (Co), copper (Cu), nickel (Ni),combinations thereof, and/or other suitable materials. The high-kdielectric layer 122 may include hafnium oxide (HfO₂). Other examples ofhigh-k dielectrics include hafnium silicon oxide (HfSiO), hafniumsilicon oxynitride (HfSiON), hafnium tantalum oxide (HMO), hafniumtitanium oxide (HMO), hafnium zirconium oxide (HfZrO), combinationsthereof, and/or other suitable materials. In various embodiments of thepresent disclosure, a metal layer 126 may be formed between the high-kdielectric layer 122 and the metal gate electrode 124. The metal layer126 may be any metal material suitable for forming a metal gate orportion thereof, including work function layers, liner layers, interfacelayers, seed layers, adhesion layers, barrier layers, etc. The metallayer 126 formed on the high-k dielectric layer may include one or moremetal layers including Ti, TiN, TaN, Ta, TaC, TaSiN, W, WN, MoN, MoON,and other suitable materials. Examples of the metal material that may bedeposited include P-type metal materials and N-type metal materials.P-type metal materials may include compositions such as ruthenium,palladium, platinum, cobalt, nickel, and conductive metal oxides, and/orother suitable materials. N-type metal materials may includecompositions such as hafnium, zirconium, titanium, tantalum, aluminum,metal carbides (e.g., hafnium carbide, zirconium carbide, titaniumcarbide, aluminum carbide), aluminides, and/or other suitable materials.The spacers 130 are next to the metal gate structure 120 and each ofthem has a skirting part 132 extending into the metal gate structure120. The skirting parts 132 contact the substrate 110. In someembodiments, a shape of the skirting part 132 is triangle. The skirtingpart 132 has a bottom angle θ, wherein the bottom angle θ is in a rangeabout 1° to about 89°. In some embodiments, the bottom angle θ is in arange about 20° to about 70°. For example, the bottom angle θ is 60°. Insome embodiments, the skirting part 132 extending into the high-kdielectric layer 122. And the skirting part 132 contacts the substrate110. In some embodiments, the spacers 130 may include silicon oxide,silicon nitride, silicon oxynitride, silicon carbide, fluoride-dopedsilicate glass (FSG), a low k dielectric material, combinations thereof,and/or other suitable material. The epitaxy 140 is next to the spacer130. The epitaxy 140 may include silicon or silicon germanium (SiGe). Insome embodiments, the epitaxy may be doped with boron and/or BF₂, orphosphorous and/or arsenic. The spacer 130 having the skirting part 132may protect the metal gate structure 120. The spacer 130 is in directcontact with the substrate 110, which means there have no gatedielectric layer between the spacer 130 and the substrate 110, thereforemay prevent the metal leakage issue. The skirting part 132 prolongs adistance between the metal gate structure 120 and the epitaxy 140, whichmay prevent an etchant etch through the spacers, make the semiconductorstructure has better reliability.

In some embodiments, the semiconductor structure may be a portion of afin type field effect transistor (FinFET). The FinFET has a thin finextending from the substrate. The channel of the FinFET is formed inthis vertical fin. And a gate is formed over (e.g., wrapping) the fin.In some embodiments, the FIG. 1 is a cross-sectional view along the finof the FinFET. The substrate 110 may be a fin, and a metal gatestructure 120 formed over a portion of the fin. Two spacers 130 adjacentto the metal gate structure 120 having a skirting part 132 extendinginto the metal gate structure 120. And two epitaxies 140 formed in thefin 110 next to the spacers 130. The metal gate structure 120 mayinclude a high-k dielectric layer 122, and a metal electrode 124. Insome embodiments, a metal layer is formed between the high-k dielectriclayer 122 and the metal electrode 124. The skirting parts 132 contactthe substrate 110. In some embodiments, a shape of the skirting part 130is triangle. The skirting part 130 has a bottom angle θ, wherein thebottom angle θ is in a range about 10° to about 80°. For example, thebottom angle θ is 60°. In some embodiments, the skirting part 132extending into the high-k dielectric layer 122. The skirting part 132 ofthe spacer 130 may decrease the metal leakage issue, which is the metalin the metal gate structure 120 leak through or under the spacers 130 tothe epitaxy 140.

Referring to FIGS. 2A-2I, FIGS. 2A-2I are various cross-sectional viewsof a method of fabricating a semiconductor structure, in accordance withsome embodiments. Referring to FIG. 2A, a gate dielectric layer 210 isformed on a substrate 200, and a dummy gate stack 220 is formed on thegate dielectric layer 210. The substrate 200 may include various dopingconfigurations depending on design requirements as is known in the art(e.g., p-type substrate or n-type substrate). The substrate 200 mayinclude various doped regions, such as source/drain regions, n-well,p-well, and may include shallow trench isolation (STI) regions. Thesubstrate 200 may include a compound semiconductor such as, siliconcarbide, gallium arsenide, indium arsenide, or indium phosphide. Thegate dielectric layer 210 may be silicon oxide (SiO₂), silicon nitride(Si₃N₄), silicon oxynitride (SiON), hafnium oxide (HfO), titaniumnitride (TiN), or combinations thereof. The gate dielectric layer 210may be formed by thermal oxidation or deposition, such as chemical vapordeposition (CVD), atomic layer deposition (ALD), and/or other suitableprocess. The dummy gate stack 220 may include a dummy gate layer 230 onthe gate dielectric layer 210, a first hard mask layer 240 on the dummygate layer 230, and a second hard mask layer 250 on the first hard masklayer 240. The dummy gate layer 230 may include polysilicon, silicon,silicon nitride, or other suitable materials. The dummy gate layer 230may be formed by CVD, PVD, or any suitable methods. The first hard masklayer 240 may include silicon oxide, silicon nitride, siliconoxynitride, silicon carbide, and/or other suitable materials. The firsthard mask layer 240 may be formed using methods such as CVD, PVD, orALD. The second hard mask layer 250 may include may include siliconoxide, silicon nitride, silicon oxynitride, silicon carbide, and othersuitable materials. The second hard mask layer 250 may be formed usingmethods such as chemical vapor deposition CVD, PVD, or ALD.

Referring to FIG. 2B, a dummy gate structure 320 is formed. The dummygate stack 220 in FIG. 2A is etched to form the dummy gate structure320. The etching process may include a photolithography and developingprocess. The etching method may be a dry etching or a wet etching. Insome embodiments, the etching method is dry etching, and a gas in thedry etching is selected from a group consisting of HBr, CF₄, CHF₃, CH₄,CH₂F₂, N₂H₂, BCl₃, SF₆, Cl₂, N₂, H₂, O₂, He, Ar and combinationsthereof. The dry etching may be operated under a pressure in a rangeform about 1 to about 80 mtorr, a power in a range form about 100 toabout 1000 W, and a temperature in a range form about 10 to about 65° C.

Referring to FIG. 2C, the gate dielectric layer 210 is etched, and arecess 420, is formed. Part of the gate dielectric layer 210 is etchedto form the gate dielectric layer 410 and the recess 420 under the dummygate structure 320. In some embodiments, the recess 420 may have arecess angle α. The recess angle α is in a range about 1° to about 89°.In some embodiments, the recess angle α is in a range about 20° to about70°. For example, the recess angle α is 60°. The recess 420 may beformed by dry etching. In some embodiments, the gas in the dry etchingis selected from a group consisting of HBr, CF₄, CHF₃, CH₄, CH₂F₂, N₂H₂,BCl₃, Cl₂, N₂, H₂, O₂, He, Ar and combinations thereof. The dry etchingmay be operated under a pressure in a range form about 1 to about 80mtorr, a power in a range form about 100 to about 1500 W, and atemperature in a range form about 10 to about 65° C.

Referring to FIG. 2D, a protection layer 510 surrounding the dummy gatestructure 320 is formed. And the protection layer 510 fills the recess420. The protection layer 510 may be formed by deposition. For example,the deposition process may be CVD, PVD, ALD, or any suitable methods. Insome embodiments, part of the protection layer 510 on the substrate maybe etched, only the part of the protection layer 510 surrounding thedummy gate structure 320 is left. The protection layer 510 may includesilicon oxide, silicon nitride, silicon oxynitride, silicon carbide,fluoride-doped silicate glass (FSG), a low k dielectric material,combinations thereof, or other suitable material. And the material ofthe protection layer 510 is different from the gate dielectric layer.

Referring to FIG. 2E, an epitaxy 610 is formed next to the protectionlayer 510. In some embodiments, the epitaxy 610 may be formed by etchingthe substrate 200 next to the protection layer 510 to form a cavity 620,then growing epitaxy 610 in the cavity 620. The etching process may be adry etching, a wet etching, or a combination thereof, for example a dryetching first, and then a wet etching performed may form a cavity with adiamond shape. After the cavity 620 is formed, an epitaxial (epi)process is performed to form the epitaxy 610 in the cavity 620. The epiprocess may include a selective epitaxy growth (SEG) process, cyclicdeposition and etching (CDE) process, chemical vapor deposition (CVD)techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD(UHV-CVD)), molecular beam epitaxy (MBE), other suitable epi processes,and/or combination thereof. The epi process may use gaseous and/orliquid precursors, which may interact with the composition of thesubstrate 200. The epitaxy 610 may include silicon or silicon germanium(SiGe). In some embodiments, the epitaxy may be doped with boron and/orBF₂, or phosphorous and/or arsenic. In some embodiments, the epitaxy 610may have a diamond shape or a hexagonal shape.

Referring to FIG. 2F, an inter-layer dielectric (ILD) layer 720 isdeposited over the substrate 200. And the dummy gate layer 330 isexposed, and two spacers 710 are formed. The ILD layer 720 may includesilicon oxide, silicon oxynitride, flowable oxide, or a low k material.In some embodiments, the ILD layer 720 is formed by deposition, such aschemical vapor deposition (CVD), high density plasma CVD, spin-on,sputtering, or other suitable methods. In a gate last process, the dummygate structure 320 may be removed so that a resulting metal gatestructure may be formed in place of the dummy gate structure 320.Accordingly, the ILD layer 720 may be planarized by a chemicalmechanical polishing (CMP) process until a top portion of the dummy gatelayer 330 is reached as illustrated in the figure. Therefore, the dummygate layer 330 is exposed by the CMP process. In some embodiments, partof the ILD layer 720, part of the protection layer 510, the first hardmask layer 340 and the second hard mask layer 350 are removed. In someembodiments, part of the dummy gate layer 330 is also removed. And thetwo spacers 710 are formed from the protection layer 510. The spacer 710includes a skirting part 730. The skirting part 730 contact thesubstrate 200. In some embodiments, a shape of the skirting part 730 istriangle. The skirting part 730 has a bottom angle θ, wherein the bottomangle θ is in a range about 1° to about 89°. In some embodiments, thebottom angle θ is in a range about 20° to about 70°. For example, thebottom angle θ is 60°. In some embodiments, the skirting part 730extending into the gate dielectric layer 410. In some embodiments, thespacers include silicon oxide, silicon nitride, silicon oxynitride,silicon carbide, fluoride-doped silicate glass (FSG), a low k dielectricmaterial, combinations thereof, or other suitable material.

Referring to FIG. 2G, the dummy gate layer 330 is removed. The dummygate layer 330 may be removed by a dry etching or a wet etching. Thedummy gate layer 330 is etched out, and a trench 800 is formed betweenthe spacers 710. Within the trench 800, a metal gate structure may beformed in following operations. In some embodiments, the dummy gatelayer 330 is selectively etched by a wet etch process including exposureto a hydroxide containing solution (e.g., ammonium hydroxide), deionizedwater, and/or other suitable etchant solutions.

Referring to FIG. 2H, the gate dielectric layer 410 is removed. The gatedielectric layer 410 may be removed by a dry etching or a wet etching.The spacer 710 having the skirting part 730 may prevent the etchantetching through the spacer 710. The spacers 710 are directly contact tothe substrate 200, therefore no gate dielectric layer 410 is remainedunder the spacers 710, and no tunnel under the spacers may be formedduring the etching operation. Therefore no metal leakage issue may beformed in the following operations.

Referring to FIG. 2I, a metal gate structure 900 is formed between thespacers 710. The metal gate structure 900 may formed by a depositionprocess, such as CVD, PVD, plating, or other suitable processes. In someembodiments, the metal gate structure 900 includes a high-k dielectriclayer 910 on the substrate 200, a metal layer 920 formed on the high-kdielectric layer 910, and a metal gate electrode 930 on the metal layer920. The metal gate electrode 930 may include, tungsten (W), aluminum(Al), titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalumnitride (TaN), cobalt (Co), copper (Cu), nickel (Ni), combinationsthereof, and/or other suitable materials. The high-k dielectric layer910 may include hafnium oxide (HfO₂). Other examples of high-kdielectrics include hafnium silicon oxide (HfSiO), hafnium siliconoxynitride (HfSiON), hafnium tantalum oxide (HMO), hafnium titaniumoxide (HMO), hafnium zirconium oxide (HfZrO), combinations thereof,and/or other suitable materials. The metal layer 920 may be any metalmaterial suitable for forming a metal gate or portion thereof, includingwork function layers, liner layers, interface layers, seed layers,adhesion layers, barrier layers, etc. The metal layer 126 formed on thehigh-k dielectric layer may include one or more metal layers includingTi, TiN, TaN, Ta, TaC, TaSiN, W, WN, MoN, MoON, and/or other suitablematerials. Examples of the metal material that may be deposited includeP-type metal materials and N-type metal materials. P-type metalmaterials may include compositions such as ruthenium, palladium,platinum, cobalt, nickel, and conductive metal oxides, and/or othersuitable materials. N-type metal materials may include compositions suchas hafnium, zirconium, titanium, tantalum, aluminum, metal carbides(e.g., hafnium carbide, zirconium carbide, titanium carbide, aluminumcarbide), aluminides, and/or other suitable materials. After the metalgate structure 900 formed, a CMP process is performed to remove part ofthe high-k dielectric layer, the metal layer, and the metal electrode onthe ILD layer. The spacers 710 have a skirting part 730 extending intothe metal gate structure 900, and the skirting parts 730 contact thesubstrate 200. The skirting part 730 may prevent metal leakage duringthe operation for forming the metal gate structure 900.

Referring to FIG. 3, FIG. 3 is a flowchart of the method of fabricatinga semiconductor structure, in accordance with some embodiments. Themethod 360 begins with block 362 in which a gate dielectric layer and adummy gate stack are formed on a substrate. In some embodiments, thesubstrate may be a silicon substrate. In some embodiments, the dummygate stack includes a dummy gate layer deposited on the gate dielectriclayer, a first hard mask layer deposited on the dummy gate layer, and asecond hard mask layer deposited on the first hard mask layer. And thegate dielectric layer may be formed by thermal oxidation or deposition.The method 360 continues with block 364 in which the dummy gate stack isetched to form a dummy gate structure. Then the method 360 continueswith block 366 in which the gate dielectric layer is etched to form arecess under the dummy gate structure. In some embodiments, the etchingprocess is dry etching, and a gas in the dry etching is selected from agroup consisting of HBr, CF₄, CHF₃, CH₄, CH₂F₂, N₂H₂, BCl₃, Cl₂, N₂, H₂,O₂, He, Ar or combination thereof. In some embodiments, the recess has arecess angle α in a range about 1° to about 89°. The method 360continues with block 368 in which a protection layer surrounding thedummy gate structure is formed. And the protection layer fills therecess. The method 360 continues with block 370 in which an epitaxy nextto the protection is formed. Which includes etching the substrate nextto the protection layer to form a cavity, and growing an epitaxy in thecavity. In some embodiments, the method 360 further includes depositingan ILD layer over the substrate. The method 360 continues with block 372in which a spacer having a skirting part is formed from the protectionlayer. And the dummy gate layer is exposed by a CMP process, which meanspart of the ILD layer, part of the protection layer, the first hardmasklayer and the second hardmask layer are removed. The method 360continues with block 374 in which the dummy gate structure on the gatedielectric layer is removed. Which includes etching out the dummy gatelayer. The method 360 continues with block 376 in which the gatedielectric layer is removed. The method 360 continues with block 378 inwhich the metal gate structure is formed between the spacers. The metalgate structure may be formed by deposition, which may include a high-kdielectric layer deposited on the substrate, a metal layer deposited onthe high-k dielectric layer, and a metal electrode deposited on themetal layer. The method 360 may prevent metal leakage issue when formingthe metal gate structure.

In summary, a gate last process may be implemented to form metal gatestructures. Problems with forming the metal gate structure may bereduced by etching the gate dielectric layer to form a recess under thedummy gate structure. Therefore the spacers formed next to the dummygate structure may have skirting part extending into the dummy gatestructure, and the skirting parts are directly contacted to thesubstrate. The dummy gate structure finally may be replaced by the metalgate structure. And the spacer having skirting part may help to decreasethe metal leakage issue during replacing the metal gate structure. Theskirting part may prevent the etchant etch through the spacers, make thesemiconductor structure has better reliability.

According to other various embodiments of the present disclosure, amethod of fabricating a semiconductor structure including forming a gatedielectric layer and a dummy gate stack on a substrate. The dummy gatestack is etched to form a dummy gate structure. The gate dielectriclayer is etched to form a recess that extends into the gate dielectriclayer under the dummy gate structure. A protection layer is formedsurrounding the dummy gate structure and filling the recess. A cavity isformed adjacent to the dummy gate structure by etching the substrate anda portion of the protection layer such that the protection layer has aninner-beveled part. An epitaxy is formed in the cavity next to theprotection layer. A spacer is formed from the protection layer. Thespacer includes a skirting part beneath the dummy gate structure and theinner-beveled part contacting the epitaxy. The dummy gate structure onthe gate dielectric layer is removed. A metal gate structure is formedadjacent to the spacer.

According to other various embodiments of the present disclosure, asemiconductor structure includes a substrate, a pair of epitaxies, ametal gate structure, a pair of spacers, and an inter-layer dielectriclayer. The epitaxies are over the substrate. The metal gate structure isbetween the epitaxies and includes a dielectric layer and a metal gate.The dielectric layer is over the substrate. The metal gate is over thedielectric layer. Each of the spacers has a skirting part that extendsinto the dielectric layer. A distance between the skirting parts is lessthan a distance between the epitaxies. The inter-layer dielectric layeris over the substrate and in contact with the spacers on the sidewall.

According to other various embodiments of the present disclosure, thesemiconductor structure includes a substrate, a metal gate structure,and a spacer. The metal gate structure includes a dielectric layer and ametal gate. The dielectric layer is over the substrate. The metal gateis over the dielectric layer. The spacer has a skirting part in contactwith the metal gate and extending into the dielectric layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating a semiconductorstructure, comprising: forming a gate dielectric layer and a dummy gatestack on a substrate; etching the dummy gate stack to form a dummy gatestructure; etching the gate dielectric layer to form a recess thatextends into the gate dielectric layer under the dummy gate structure;forming a protection layer surrounding the dummy gate structure andfilling the recess; forming a cavity adjacent to the dummy gatestructure by etching the substrate and a portion of the protection layersuch that the protection layer has an inner-beveled part; forming anepitaxy in the cavity next to the protection layer; forming a spacerfrom the protection layer, wherein the spacer includes a skirting partbeneath the dummy gate structure and the inner-beveled part contactingthe epitaxy; removing the dummy gate structure on the gate dielectriclayer; and forming a metal gate structure adjacent to the spacer.
 2. Themethod of claim 1, further comprising forming an inter-layer dielectriclayer in contact with the epitaxy and the protection layer.
 3. Themethod of claim 1, wherein etching the gate dielectric layer to form therecess comprises removing a portion of the gate dielectric layer exposedfrom the dummy gate structure and a portion of the gate dielectric layerunderneath the dummy gate structure by performing an etching process. 4.The method of claim 3, wherein the etching process is a dry etchingprocess.
 5. The method of claim 1, wherein forming the spacer from theprotection layer comprises removing a portion of the protection layer toexpose the dummy gate structure.
 6. The method of claim 1, wherein thegate dielectric layer and the protection layer are made of differentmaterials.
 7. The method of claim 1, wherein forming the gate dielectriclayer on the substrate includes performing thermal oxidation.
 8. Themethod of claim 1, wherein the skirting part has a triangular crosssection profile.
 9. The method of claim 1, wherein the substratecomprises a fin, and the skirting part is in contact with the fin. 10.The method of claim 1, wherein forming the metal gate structurecomprises: forming a metal layer over the gate dielectric layer; andforming a metal electrode over the metal layer.
 11. The method of claim1, wherein the gate dielectric layer has a trapezoid cross sectionprofile.
 12. A method comprising: forming a gate dielectric layer and adummy gate structure on a substrate; etching the gate dielectric layerto form a first recess that extends under the dummy gate structure;forming a spacer layer on the dummy gate structure and filling the firstrecess; etching the substrate and a portion of the spacer layer to forma second recess in the substrate and the spacer layer such that thespacer layer has an inner-beveled part; epitaxially growing asource/drain region in the second recess; etching the spacer layer toform a spacer, wherein the spacer includes a first portion beneath thedummy gate structure, the spacer further including the inner-beveledpart contacting the source/drain region; and replacing the dummy gatestructure with a metal gate structure.
 13. The method of claim 12further comprising: forming a dielectric layer over the dummy gatestructure, the spacer, and the source/drain region, the dielectric layercontacting the source/drain region.
 14. The method of claim 13, whereinreplacing the dummy gate structure comprises: planarizing the dielectriclayer to expose a top surface of the dummy gate structure; removing thedummy gate structure; and forming the metal gate structure.
 15. Themethod of claim 12, wherein etching the gate dielectric layer comprisesa dry etching process.
 16. The method of claim 12, wherein etching thespacer layer to form the spacer comprises removing a portion of thespacer layer to expose the dummy gate structure.
 17. The method of claim12, wherein the gate dielectric layer and the spacer layer havedifferent material compositions.
 18. A method comprising: forming a gatedielectric layer and a dummy gate structure on a substrate; etching thegate dielectric layer, the etching recessing the gate dielectric layerto have sidewalls underlying the dummy gate structure; forming a firstdielectric layer on the dummy gate structure, wherein the firstdielectric layer extends under the dummy gate structure to contact theetched gate dielectric layer; forming a first recess in the firstdielectric layer and in the substrate adjacent the first dielectriclayer, wherein after forming the first recess, the first dielectriclayer has an inner-beveled part; epitaxially growing a source/drainregion in the first recess, the source/drain region contacting the firstdielectric layer; etching the first dielectric layer to form a spacer,wherein the spacer includes a first portion beneath the dummy gatestructure, the spacer further including the inner-beveled partcontacting the source/drain region; forming a second dielectric layerover the dummy gate structure, the spacer, and the source/drain region,the second dielectric layer contacting the source/drain region;planarizing the second dielectric layer to expose a top surface of thedummy gate structure; and replacing the dummy gate structure with ametal gate structure.
 19. The method of claim 18, wherein the firstportion of the spacer has a triangular cross section profile.
 20. Themethod of claim 18, wherein the substrate comprises a fin, and the firstportion is in contact with the fin.